Currently, there are dozens of flue gas desulfurization technologies. Flue gas desulfurization processes are categorized into three main types: wet, semi-dry, and dry, depending on whether water is added during the desulfurization process and the dry or wet form of the desulfurized products. Wet desulfurization technology is relatively mature, highly efficient, and easy to operate. Since 1957, SDP’s wear-resistant mortar pumps have been widely used in processes such as slurry circulation, slag removal, and emergency water treatment. They are stable, reliable, safe, efficient, corrosion-resistant, and wear-resistant, with extensive application experience.
Figure: SDP’s wear-resistant pumps used in flue gas desulfurization in the power plant of a large chemical plant.
一、Wet flue gas desulfurization technology
Advantages: Wet flue gas desulfurization (FGD) technology uses a gas-liquid reaction, resulting in fast reaction speeds and high desulfurization efficiencies, generally exceeding 90%. The technology is mature and widely applicable. Wet FGD technology is relatively mature, safe and reliable in production and operation, and consistently dominates among various desulfurization technologies, accounting for over 80% of total installed desulfurization capacity.
Disadvantages: The product, which is liquid or sludge, is difficult to handle. The equipment is highly corrosive, requiring reheating of the flue gas after scrubbing. This leads to high energy consumption, large floor space requirements, and high investment and operating costs. The system is complex, the equipment is bulky, water consumption is high, and the initial investment is high. It is generally suitable for large power plants.
Classification: Commonly used wet FGD technologies include the limestone-gypsum method, the indirect limestone-gypsum method, and the lemon absorption method.
A. Limestone/lime-gypsum method:
Principle: Limestone or lime slurry absorbs SO2 in flue gas, producing calcium sulfite. The separated calcium sulfite (CaSO3) can be discarded or oxidized to calcium sulfate (CaSO4) for recovery as gypsum. This is currently the most technologically mature and stable desulfurization process in the world, achieving a desulfurization efficiency exceeding 90%.
Currently, the traditional limestone/lime-gypsum flue gas desulfurization process is widely used in the Chinese market. This process uses a calcium-based desulfurizer to absorb sulfur dioxide, producing calcium sulfite and calcium sulfate. Due to their low solubility, these calcium sulfite and calcium sulfate are prone to scaling and clogging within the desulfurization tower and pipelines. Compared to limestone-based desulfurization technology, the dual-alkali flue gas desulfurization process overcomes the scaling disadvantage of the limestone-lime method.
B. Indirect Limestone-Gypsum Method:
Common indirect limestone-gypsum methods include the sodium-alkali dual-alkali method, the alkaline aluminum sulfate method, and the dilute sulfuric acid absorption method. Principle: Sodium alkali, alkaline alumina (Al2O3·nH2O), or dilute sulfuric acid (H2SO4) absorbs SO2. The resulting absorption liquid reacts with limestone, regenerating it and producing gypsum. This method is simple to operate, produces minimal secondary pollution, avoids scaling and clogging, and offers high desulfurization efficiency. However, the resulting gypsum product is of poor quality.
C. Lemon Absorption Method:
Principle: Citric acid (H3C6H5O7·H2O) solution has excellent buffering properties. When SO2 gas passes through the citrate solution, the SO2 in the flue gas reacts with hydrogen in the water to form an H2SO3 complex, resulting in a SO2 absorption rate exceeding 99%. This method is only suitable for low-SO2 flue gas concentrations, not for high-SO2 gas absorption, and has a relatively narrow application range.
Other wet flue gas desulfurization technologies include seawater desulfurization, ammonium phosphate compound fertilizer, and liquid-phase catalytic desulfurization.
- Limestone (Lime)-Gypsum Wet Flue Gas Desulfurization Process
The limestone (lime)-gypsum desulfurization system consists of several components: a flue gas heat exchange system, an absorber desulfurization system, a desulfurization slurry preparation system, a calcium sulfite oxidation system, and a gypsum dehydration system. This process is currently the most mature and widely used technology in the world. The desulfurization process is as follows: Flue gas passes through a dust collector and a heat exchange system before entering the desulfurization tower. In the absorber, it comes into contact with a lime emulsion. The slurry absorbs SO2 in the flue gas, producing CaSO3. This slurry is then oxidized to CaSO4, i.e., gypsum, in the CaSO3 oxidation system. This process boasts a desulfurization efficiency exceeding 95%, a wide range of applications, mature technology, and stable operation. It is one of the preferred desulfurization methods for large and medium-sized coal-fired power plants.
The process flow is shown in the figure:
2. Flue gas desulfurization process using magnesium oxide-magnesium sulfate heptahydrate recovery method
The basic principle of magnesium oxide desulfurization is similar to that of limestone (lime) method, that is, magnesium oxide slurry absorbs SO2 in flue gas, mainly producing trihydrate and polyhydrate magnesium sulfite, which is then oxidized to produce stable and dissolved magnesium sulfate, and then the magnesium sulfate is concentrated and crystallized to finally produce MgSO4·7H2O product. The brief process flow is shown in the figure below.
- Dual-Alkali Flue Gas Desulfurization Process
The dual-alkali process uses a soluble alkaline solution as an absorbent to absorb SO2 in an absorption tower. Most of the absorbent is then discharged and regenerated with lime milk.
Because two different types of alkali are used in the absorption and absorption liquid treatment, it is called the dual-alkali process. Dual-alkali processes include various dual-alkali processes, such as sodium-calcium, magnesium-calcium, and calcium-calcium. The sodium-calcium dual-alkali process is one of the more commonly used desulfurization methods, successfully applied in power plants and industrial boilers.
- Wet Ammonia Flue Gas Desulfurization Process
The ammonia desulfurization process uses ammonia as an absorbent to remove SO2 from flue gas. The process generally consists of three steps: sulfur absorption, intermediate product processing, and by-product production. Depending on the process and by-products, it can be further categorized as the ammonia-ammonium sulfate fertilizer process, the ammonia-ammonium phosphate fertilizer process, the ammonia-acid process, and the ammonia-ammonium sulfite process.
The process mainly consists of desulfurization and washing system, concentration system, flue gas system, ammonia storage system, ammonium sulfate production system (if it is not the ammonia-ammonium sulfate method, it is the by-product manufacturing system corresponding to its process), electrical automatic control system, etc.
- Carbide Slag-Gypsum Flue Gas Desulfurization Process
Calcium carbide is an important raw material in the organic synthesis industry, primarily used in the production of acetylene, further producing chemical products such as polyvinyl chloride (PVC), vinyl acetate (VAc), and chloroprene rubber (CR), as well as metal processing (cutting and welding, etc.). Carbide slag is the waste residue generated during the production of acetylene from calcium carbide. Its main components include calcium(OH)2, as well as metal oxides and hydroxides such as Fe2O3, SiO2, and Al2O3, as well as small amounts of organic matter.
The large amount of calcium(OH)2 contained in carbide slag is strongly alkaline, making it an excellent sulfur dioxide absorbent. Test results show that the desulfurization capacity of carbide slag is 20% higher than that of commercial calcium(OH)2, while the product cost is only one-third of that of commercial calcium(OH)2.
The process flow is essentially the same as the limestone-gypsum process, comprising a flue gas system, desulfurizer preparation system, absorption circulation system, by-product treatment, and electrical automatic control systems.
6. Papermaking White Mud-Gypsum Flue Gas Desulfurization Process
The main components of papermaking white mud are CaCO₃, MgO, and SiO₂. CaCO₃ and MgO are highly soluble in water and alkaline when dissolved in water, making them the primary desulfurization agents. Because they contain multiple alkaline components such as Ca, Mg, and Na, their overall desulfurization performance is significantly superior to that of limestone/lime powder alone.
The process flow is essentially the same as the limestone-gypsum method, encompassing a flue gas system, desulfurization agent preparation system, absorption and circulation system, by-product treatment, and electrical automatic control systems.
Dry Flue Gas Desulfurization Technology
Advantages: Dry flue gas desulfurization technology involves a gas-to-gas reaction. Compared to wet flue gas desulfurization systems, it offers simpler equipment, a smaller footprint, lower investment and operating costs, easier operation, lower energy consumption, easier product disposal, and no wastewater treatment system.
Disadvantages: However, the reaction rate is slow, resulting in low desulfurization rates, though advanced technologies can reach 60-80%. However, this method currently suffers from low desulfurization efficiency, low absorbent utilization, severe wear and scaling, and significant equipment maintenance difficulties. The equipment also suffers from low operational stability and reliability, and a short lifespan, limiting its application.
Classification: Common dry flue gas desulfurization technologies include activated carbon adsorption, electron beam irradiation, charged dry absorbent injection, and metal oxide desulfurization.
Typical dry desulfurization systems inject a desulfurizer (such as limestone, dolomite, or slaked lime) directly into the furnace. Taking limestone as an example, when calcined at high temperatures, the desulfurizer forms porous calcium oxide particles, which react with SO₂ in the flue gas to form calcium sulfate, achieving the desulfurization goal.
Dry flue gas desulfurization technology has been used in large converters and blast furnaces in the steel industry, but it is less suitable for small and medium-sized blast furnaces. The advantages of dry desulfurization technology include a simple process, no wastewater or acid disposal issues, low energy consumption, and, in particular, a high flue gas temperature after purification, which facilitates chimney exhaust diffusion and eliminates “white smoke.” Purified flue gas does not require secondary heating and is less corrosive. However, its disadvantages include low desulfurization efficiency, large equipment size, high investment, large floor space requirements, and high operational skills. Common dry desulfurization technologies include:
Industrial Kilns A. Activated Carbon Adsorption Method:
Principle: SO₂ is adsorbed by activated carbon and catalytically oxidized to sulfur trioxide (SO₃), which then reacts with water to form H₂SO₄. The saturated activated carbon can be regenerated by washing or heating, simultaneously producing dilute H₂SO₄ or highly concentrated SO₂. The byproducts produced are H2SO4, liquid SO2, and elemental sulfur, effectively controlling SO2 emissions while also recovering sulfur resources. Xi’an Jiaotong University has refined this technology, developing the low-cost, highly selective adsorption ZL30 and ZIA0 activated carbons. This further refines the activated carbon process, achieving a SO2 adsorption rate of 95.8% in flue gas, meeting national emission standards.
B. Electron Beam Irradiation Method:
Principle: High-energy electron beams are used to irradiate flue gas, generating a large amount of reactive species that oxidize SO2 and nitrogen oxides in the flue gas into SO3 and nitrogen dioxide (NO2). H2SO4 and nitric acid (NaNO3) are then generated, which are then absorbed by ammonia (NH3) or limestone (CaCO3) absorbents.
C. Charged Dry Absorbent Injection Desulfurization Method (CD-SI):
Principle: Absorbent flows at high speed through a high-voltage electrostatic corona charging zone generated by an injection unit, imparting an electrostatic charge to the absorbent. When the absorbent is injected into the flue gas stream, the like-charged absorbents repel each other, exposing their surfaces and significantly improving desulfurization efficiency. This method is a dry treatment method, resulting in no equipment pollution or scaling, no wastewater or waste residue, and byproducts that can be used as fertilizer. No secondary pollutants are generated, resulting in a desulfurization rate exceeding 90%. Furthermore, the equipment is simple and widely applicable. However, this desulfurization method relies on an electron beam accelerator to generate high-energy electrons. For large-scale enterprises, this requires a high-power electron gun, which is harmful to humans and requires radiation shielding, resulting in high operation and maintenance requirements. The Chengdu Thermal Power Plant in Sichuan has installed an electron desulfurization system, which removes SO2 from flue gas and meets national emission standards.
D. Metal Oxide Desulfurization Method:
Principle: Due to the fact that SO2 is a relatively reactive gas, oxides such as manganese oxide (MnO), zinc oxide (ZnO), iron oxide (Fe3O4), and copper oxide (CuO) have a strong adsorption capacity for SO2. At room or low temperatures, metal oxides adsorb SO2. At high temperatures, the metal oxides react chemically with SO2 to form metal salts. The adsorbate and metal salts are then regenerated through thermal decomposition and washing. This is a dry desulfurization method. While it does not produce wastewater or waste acid and does not cause pollution, it has not been widely adopted due to its low desulfurization efficiency, large equipment, high investment, and high operating requirements, resulting in high costs. The key to this technology lies in the development of new adsorbents.
The aforementioned SO2 flue gas treatment technologies are currently widely used. While they offer relatively high desulfurization rates, they suffer from complex processes, high operating costs, incomplete pollution prevention, and secondary pollution. These drawbacks are inconsistent with my country’s overall goal of achieving harmonious economic and environmental development. Therefore, it is necessary to explore and research new desulfurization technologies.
III. Semi-dry Flue Gas Desulfurization Technology
Semi-dry desulfurization includes spray drying, semi-wet/dry desulfurization, powder-particle spouted bed desulfurization, and flue injection desulfurization.
A. Spray Drying:
Spray drying desulfurization utilizes mechanical or airflow forces to disperse the absorbent into extremely fine mist droplets. These droplets create a relatively large contact surface area with the flue gas, resulting in a desulfurization process involving heat exchange, mass transfer, and chemical reactions between the gas and liquid phases. Commonly used absorbents include alkali liquor, lime milk, and limestone slurry. Currently, most installations use lime milk as the absorbent. Generally, this method achieves a desulfurization rate of 65% to 85%. Advantages: Desulfurization occurs in a three-phase system of gas, liquid, and solid, requiring simple process equipment. The products are dry CaSO4 and CaSO4, which are easy to handle, without significant equipment corrosion or blockage, and with relatively low water consumption. Disadvantages: High automation requirements make it difficult to control the absorbent dosage, resulting in low absorption efficiency. Therefore, developing an appropriate absorbent is a new challenge facing this method.
B. Semi-wet/Dry Method:
The semi-wet/dry method lies between wet and dry methods, offering parameters such as desulfurization efficiency and desulfurizer utilization that fall somewhere in between. It is primarily suitable for flue gas treatment in small and medium-sized boilers. This technology features low investment and operating costs. While lower than wet desulfurization technology, desulfurization rates can still reach 70%. It is also less corrosive, requires less floor space, and is reliable. Compared to wet desulfurization systems, the commonly used semi-dry, semi-wet desulfurization system eliminates the slurrying system. Instead of spraying a Ca(OH)2+ aqueous solution in wet desulfurization systems, it instead sprays CaO or Ca(OH)2+ powder and water mist. Compared to dry desulfurization systems, this overcomes the shortcomings of in-furnace calcium injection, which often results in low SO2 and CaO reaction efficiency and long reaction time, while improving desulfurizer utilization. The process is simple and holds great promise for future development.
C. Powder-Particle Spouted Bed Semi-Dry Flue Gas Desulfurization:
Technical Principle: SO2-laden flue gas passes through a preheater and enters a powder-particle spouted bed. The desulfurizer, pre-mixed with water in powder form, is continuously sprayed into the bed as a slurry from the top. The desulfurizer mixes thoroughly with the spouted particles and, through contact with the hot flue gas, desulfurization and drying occur simultaneously. The desulfurization reaction products are discharged from the separator as dry powder. This desulfurization technology uses limestone or slaked lime as the desulfurizer. This method offers high desulfurization rates and desulfurizer utilization rates, while minimizing environmental impact. However, strict requirements exist between inlet air temperature, relative humidity within the bed, and reaction temperature. Improper control of the slurry moisture content and reaction temperature can lead to desulfurizer sticking to the wall.
D. Semi-dry Flue Gas Desulfurization with Flue Duct Injection:
This method utilizes the flue between the boiler and dust collector as a reactor for desulfurization, eliminating the need for a separate absorption vessel. This significantly reduces process investment, simplifies operation, and requires minimal site space, making it suitable for development and application in my country. Semi-dry flue gas desulfurization involves injecting an absorbent slurry into the flue. The slurry droplets evaporate and react, leaving the reaction product as a dry powder.
IV. Emerging Flue Gas Desulfurization Methods
In recent years, with rapid technological advancements, environmental issues have become a legal issue. Chinese scientists have developed several new desulfurization technologies, but most remain in the experimental stage and await further industrial application verification.
- Alkali Sulfide Desulfurization Method
Developed by Outokumpu, the alkaline sulfide desulfurization method primarily uses industrial-grade sodium sulfide as a raw material to absorb SO2 from industrial flue gas, with the goal of producing sulfur. The reaction process is quite complex, generating substances such as Na2SO4, Na2SO3, Na2S2O3, S, and Na2Sx. The products indicate high energy consumption and low-value byproducts. Research by Shi Lin of South China University of Technology has shown that the content of various sulfur compounds in the process varies with reaction conditions. By controlling the solution pH between 5.5 and 6.5 and adding a small amount of the oxidizing additive TFS, the product primarily produces Na2S2O3. Filtration and evaporation yield the high-value 5H0·Na2S2O3, with a desulfurization rate of up to 97%. The reaction process is: SO2 Na2S = Na2S2O3 S. This new desulfurization technology has passed pilot testing and is being promoted and applied.
- Membrane Absorption
Membrane separation technology, represented by organic polymer membranes, is a new gas separation technology developed in recent years and has been widely used, particularly in water purification and treatment. Researchers Jin Mei and others at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, have creatively used membranes to absorb and remove SO₂ gas, achieving remarkable results and a desulfurization rate of 90%. They utilize a polypropylene hollow fiber membrane absorber with a sodium hydroxide solution as the absorbent to remove SO₂. The unique feature of this method is that the porous membrane separates the SO₂ gas and the sodium hydroxide absorbent. The SO₂ gas then passes through the pores of the porous membrane to the gas-liquid interface, where it rapidly reacts with the sodium hydroxide, achieving desulfurization. This method, combining membrane separation and absorption technologies, offers low energy consumption, simple operation, and minimal investment.
- Microbial Desulfurization Technology
Based on the fact that microorganisms participate in various processes of the sulfur cycle and generate energy, microbial flue gas desulfurization is used. The mechanism is as follows: Under aerobic conditions, desulfurization bacteria indirectly oxidize SO2 in the flue gas into sulfuric acid, from which the bacteria obtain energy.
Compared to traditional chemical and physical desulfurization, biological desulfurization requires virtually no external conditions such as high temperature, high pressure, or catalysts; it operates at room temperature and pressure. Furthermore, the process is simple and produces no secondary pollution. Based on the removal of 5 tons of H:S per day from geothermal power plants, the total cost of microbial desulfurization was calculated to be 50% of that of conventional wet methods. Both organic and inorganic sulfur, upon combustion, can generate inorganic sulfur SO2 that can be indirectly utilized by microorganisms. Therefore, the development of microbial flue gas desulfurization technology holds great potential. Wang An and others at Sichuan University used Bacillus ferrooxidans in laboratory research, achieving a desulfurization rate of 98% at a low liquid-to-gas ratio.
V. Denitrification Technology
Common denitrification technologies can be divided into two main categories based on the formation mechanism of nitrogen oxides:
One is source control, controlling NOx generation during calcination. Technical measures include: ① Using low-NOx burners; ② Staged combustion within the decomposition furnace and pipelines to control combustion temperature; ③ Changing the batching scheme and using mineralizers to reduce the clinker calcination temperature.
The other is end-of-pipe control, controlling NOx emissions from flue gas. Technical measures include: ① “Staged Combustion (SNCR)” (for which pilot projects have been conducted in China); ② Selective Non-Catalytic Reduction (SNCR) (for which pilot projects have been conducted in China); ③ Selective Catalytic Reduction (SCR) (for which only three pilot lines are currently underway in Europe); ③ Combined SNCR/SCR denitrification technology (for which there is no successful experience in cement denitrification in China); and ④ Biological denitrification technology (currently in the research and development stage).
Domestic denitrification technologies are still in the exploratory and demonstration stage, and scientific research has yet to be conducted. Are the various design, process, technical routes, and equipment and facilities scientifically sound and reliable in operation? Denitrification efficiency, operating costs, energy consumption, and the amount of secondary pollutant emissions will all be tested in practice. Denitrification technologies can be specifically divided into: Denitrification before combustion: (1) Hydrogenation denitrification, (2) Washing Denitrification during combustion: (1) Low-temperature combustion, (2) Low-oxygen combustion, (3) FBC combustion technology, (4) Use of low-NOx burners, (5) Coal powder separation, (6) Flue gas recirculation technology Denitrification after combustion: (1) Selective non-catalytic reduction denitrification (SNCR), (2) Selective catalytic reduction denitrification (SCR), (3) Activated carbon adsorption, (4) Electron beam denitrification technology 1. Selective catalytic reduction (SCR) denitrification technology The SCR denitrification process uses a catalyst to mix NOx in the flue gas with ammonia from the reducing agent supply system at a certain temperature (270~400℃) to produce nitrogen and water, thereby reducing NOx emissions and alleviating the pollution of flue gas to the environment. The reducing agent used in the SCR reaction can be liquid ammonia, aqueous ammonia (25% NH3), or urea.
The SCR denitrification process system can be divided into a liquid ammonia storage and transportation system (liquid ammonia as the reducing agent), an ammonia preparation and supply system, an ammonia/air mixing system, an ammonia injection system, a flue gas system, an SCR reactor system, and an ammonia emergency treatment system.
- Selective Non-Catalytic Reduction (SNCR) Denitrification Technology
The SNCR method primarily involves injecting a nitrogen-containing reducing agent (urea, aqueous ammonia, or liquid ammonia) into flue gas at a temperature of 850-1100°C, causing a reduction reaction that removes NOx and produces nitrogen and water. Because nitrogen-containing reducing agents are selective for NOx reduction within a certain temperature range and in the presence of oxygen, and because the reaction does not require a catalyst, it is called selective non-catalytic reduction. The main equipment of the SNCR system adopts a modular design, consisting of a reducing agent storage and delivery module, a dilution water module, a mixing and metering module, and an injection module.
3. SNCR-SCR Combined Denitrification Technology
The SNCR/SCR combined process combines SNCR and SCR technologies. Urea, or a similar reducing agent, is used in the high-temperature zone of 850-1100°C in the upper furnace. The reducing agent is precisely distributed to each spray gun via a metering and delivery system. The reducing agent is then sprayed into the furnace to remove NOx. Excess ammonia escapes with the flue gas and enters the SCR denitrification reactor, which is equipped with a small amount of catalyst, after the furnace, achieving secondary denitrification.
The SNCR/SCR hybrid denitrification system primarily consists of a reducing agent storage and preparation system, delivery system, metering and delivery system, injection system, flue gas system, SCR denitrification catalyst and reactor, and electrical control system.
SNCR denitrification efficiency can reach 25%-40% for large coal-fired units and up to 80% for smaller units. Because this method is significantly affected by boiler size, it is often used as a supplemental treatment method to low-NOx combustion technologies. Its low engineering cost, simple layout, and small footprint make it suitable for retrofitting existing plants, and new plants can adapt it to their boiler designs.
Selective catalytic reduction (SCR) is currently the most mature flue gas denitrification technology. It is a post-combustion denitrification method first commercialized in Japan in the late 1960s and 1970s. It utilizes a reducing agent (NH3, urea) over a metal catalyst to selectively react with NOx to produce N2 and H2O, rather than oxidation by O2. Therefore, it is called “selective.” Currently, the two most popular SCR processes worldwide are ammonia-based SCR and urea-based SCR. Both methods utilize ammonia’s ability to reduce NOx. Under the action of a catalyst, NOx (primarily NO) is reduced to N2 and water, which have little impact on the atmosphere. The reducing agent is NH3.
Currently, catalysts used in SCR mostly use TiO2 as a carrier and V2O5, V2O5-WO3, or V2O5-MoO3 as active ingredients. They are manufactured in three types: honeycomb, plate, or corrugated. SCR catalysts used in flue gas denitrification can be divided into high-temperature catalysts (345°C to 590°C), medium-temperature catalysts (260°C to 380°C), and low-temperature catalysts (80°C to 300°C). Different catalysts have different optimal reaction temperatures. If the reaction temperature is too low, the catalyst activity will decrease, resulting in reduced denitrification efficiency. Continuous operation at low temperatures can cause permanent damage to the catalyst. If the reaction temperature is too high, NH3 is easily oxidized, increasing NOx generation. It can also cause phase changes in the catalyst material, degrading the catalyst’s activity. Currently, most SCR systems, both domestically and internationally, use high-temperature catalysts, with reaction temperatures ranging from 315°C to 400°C. The advantages and disadvantages of this method in practical applications are as follows:
Advantages: This method offers high denitrification efficiency and is relatively inexpensive. It is currently widely used in domestic and international projects and has become the mainstream technology for power plant flue gas denitrification.
Disadvantages: Fuel contains sulfur, which generates a certain amount of SO₃ during combustion. After adding a catalyst, SO₃ production increases significantly in the presence of oxygen, reacting with excess NH₃ to form NH₄HSO₄. NH₄HSO₄ is corrosive and sticky, and can damage tail flue equipment. Although SO₃ production is limited, its impact should not be underestimated. Furthermore, catalyst poisoning is a significant issue.
Application of Desulfurization and Denitrification Technologies in Industrial Kilns and Boiler Enterprises
Desulfurization and denitrification technologies for boiler enterprises in China are primarily based on coal or gas as the combustion medium. For coal-fired boilers, the most mature process in China is FGD (using absorbents or adsorbents to remove sulfur dioxide from flue gas), while denitrification is primarily based on selective catalytic reduction (SCR).
FGD Technology Comparison
SCR denitrification technology is the world’s most mainstream method for NOx removal. This method can be integrated into existing FGD processes with a denitrification unit. In an oxygen-containing atmosphere, the catalytic process in which a reducing agent reacts with a limited amount of NO in the exhaust gas is called selective catalytic reduction. Suitable catalysts and reducing agents should possess the following characteristics:
1) The reducing agent should be highly reactive.
2) The reducing agent should react selectively with NOx, while avoiding the oxidizing substances present in large quantities in the flue gas.
3) The reducing agent must be inexpensive to ensure a cost-effective removal process.
4) The catalyst should significantly lower the NOx reduction temperature.
5) The catalyst should have high catalytic activity to effectively reduce low concentrations of NOx in flue gas.
6) The catalyst should selectively react with the reducing agent and NOx to form N2, while being inert to the reaction between the reducing agent and other oxidizing species in the flue gas.
7) The catalyst should have a stable structure.
8) The catalyst should not be poisoned by other flue gas components.
For the boiler industry, simultaneous desulfurization and denitrification technology is essential. Currently, most domestic desulfurization and denitrification technologies are separate. This approach results in redundant equipment construction, high energy consumption, and high labor and operating costs. Simultaneous desulfurization and denitrification technology can, to a certain extent, avoid these problems.
Flue Gas Desulfurization Technology Development Trends
Currently available technologies each have their own advantages and disadvantages. Specific applications require a detailed analysis, with comprehensive considerations of investment, operation, and environmental protection to determine the appropriate desulfurization technology. With the advancement of science and technology, the development of a new technology often involves many different disciplines. Therefore, keeping track of the latest developments and research results in other disciplines and applying them to flue gas desulfurization (FGD) is a key approach to developing novel FGD technologies. For example, new desulfurization technologies such as microbial desulfurization and electron beam desulfurization each have significant potential for development due to their unique characteristics. With increasing attention to environmental governance and the continuous increase in industrial flue gas emissions, desulfurization technologies that offer low investment and operating costs, high desulfurization efficiency, high desulfurizer utilization, minimal pollution, and zero secondary pollution are poised to become the primary trends in FGD technology development.
While various FGD technologies have achieved certain economic, social, and environmental benefits in SO2 removal, they still have some shortcomings. With the continued advancement of biotechnology and other high-tech technologies, a range of new and highly adaptable desulfurization technologies, such as electron beam desulfurization and biological desulfurization, are poised to replace traditional desulfurization methods.